1. Field of the Invention
This invention relates to down hole drilling motors, such as turbo drills and drills operated by positive displacement motors, and to certain improved features therein.
Down hole drilling motors were first invented 100 years ago. Down hole drilling motors were first extensively tested in the 1920's. They did not find wide spread use until the 1950's when turbo drills began to be used in the Soviet Union. By the early 1960's, it is estimated that 85% of the wells in the Soviet Union were being drilled with turbo drills. Down hole drilling motors have found wide spread use in the United States for drilling directional holes, but they are not widely used for straight hole drilling because of bearing and seal problems. Commercial down hole drilling motors operate at speeds ranging from 300 to 1,000 rpm whereas, roller bits operate most effectively at speeds of 50 to 150 rpm. At high motor speeds, roller bearings fail after periods of about 5 to 15 hours whereas with conventional drilling equipment operating at lower speeds the bearings of roller bits last up to 200 hours. Down hole motors have had substantial problems in design of radial and vertical thrust bearings, lubrication systems, turbine efficiency, housing construction, etc., which have limited substantially the acceptability of down hole motors in petroleum drilling and in other applications.